Ana Baamonde1, 2, *, Marco Álvarez-Vega1, Agustín
Hidalgo2 and Luis Menéndez2
1Laboratorio de Farmacología, Departamento de Medicina, Facultad de Medicina, Universidad de Oviedo,
Julián Clavería s/n, 33006 Oviedo, Asturias, Spain
2Instituto Universitario de Oncología del Principado de Asturias, Asturias, Spain
* To whom correspondence should be addressed(1).
Abstract: We studied the effects of intraplantar morphine in the formalin test in mice. Intraplantarly administered morphine (30-300 mg) induced analgesic effects at lower doses than intraperitoneally administered morphine. Following the administration of [3H]morphine, the % of radioactivity present in brain was the same by either route. In contrast, higher radioactivity values appeared in the injected paw in those mice intraplantarly injected. Since local morphine induces analgesia at doses lower than the intraperitoneally administered drug, especially in the second phase of the test, and the access to brain is undistinguishable, we propose that local morphine enhances central opiate analgesia in the formalin test in mice.
Keywords: Peripheral analgesia, Intraplantar morphine, Formalin test